Coriolis flow meter

Abstract

The invention relates to a Coriolis flowmeter (1) comprising a measuring tube (2), an excitation system for exciting the measuring tube (2), a sensor system (4) for detecting the mechanical vibrations of the measuring tube (2), wherein the sensor system (4) is designed to generate at least one first sensor signal s1 and a second sensor signal s2, and a measuring and / or operating circuit (5) which is made of at least one microprocessor in particular, wherein the measuring and / or operating circuit (5) is designed to operate the excitation system using an excitation signal. The measuring and / or operating circuit (5) comprises a filter which has a filter coefficient α and which is designed to receive the first sensor signal s1 and generate a filtered first sensor signal s1*, and the measuring and / or operating circuit (5) comprises a second filter (7b) which has a filter coefficient b and which is designed to receive the second sensor signal s2 and generate a filtered second sensor signal s2*. The measuring and / or operating circuit (5) is designed to receive the filtered first sensor signal s1* and the second sensor signal s2, and the measuring and / or operating circuit (5) comprises a control circuit (15) which is designed to control the filter coefficient α and / or b on the basis of the filtered first sensor signal s1* and the second sensor signal s2 such that a control criterion is satisfied. The measuring α and / or b operating circuit (5) is designed to generate a first measurement value, which represents the process variable, from the filter coefficient α and / or b.

Description

[0001] Coriolis flowmeter

[0002] The invention relates to a Coriolis flowmeter for determining a time-varying process variable of a flowable medium.

[0003] Field devices for process measurement technology with a vibration-type sensor, and in particular Coriolis flowmeters, have been known for many years. The basic design of such a measuring device is described, for example, in EP 1 807 681 A1, whereby the design of a generic field device is fully incorporated by reference in this document within the scope of the present invention.

[0004] Typically, Coriolis flowmeters have at least one or more oscillating measuring tubes, which can be set into vibration by a vibration exciter. These vibrations are transmitted along the length of the tube and are varied by the type of fluid contained in the measuring tube and its flow velocity. A vibration sensor, or in particular two spaced-apart vibration sensors, can record the varied vibrations at another location in the measuring tube in the form of one or more sensor signals. A measuring and / or operating circuit can then determine the mass flow, viscosity, and / or density of the flowing medium from the sensor signal(s).

[0005] To determine the mass flow m it is common to use the following formula: m = k • tan(Ay? / 2) / 27r

[0006] Where f is the driving frequency of the excitation signal, A <p die Phasendifferenz zwischen zwei gemessenen Sensorsignalen und k ein Kalibrationsfaktor. Mit diesem Ansatz lässt sich der Massenstrom sehr genau für stabile Durchflüsse bestimmen. Nachteilig daran ist, dass sich das Messsystem bei gestörten Bedingungen - wie sie beispielsweise bei Multiphasen im Medium auftreten - und somit bei einer zeitlich instabilen Treiberfrequenz und Amplitude, nicht mehr in einem harmonischen Betriebsmodus befindet und die obige Formel nicht mehr ausreichend genau oder gar ungültig ist. Weiterhin kann es zu einem zeitlichen Versatz zwischen der ermittelten Phasendifferenz A<p und der T reiberfrequenz f kommen, d.h. dass die für den Messwert der Prozessgröße angenommene Treiberfrequenz f nicht mit der tatsächlich zum Zeitpunkt der Messung der Sensorsignale für die Ermittlung der Phasendifferenz A<p vorliegende T reiberfrequenz f übereinstimmt. Dies führt zu einer Verfälschung des ermittelten Prozessgröße.

[0007] The invention therefore has the task of remedying the problem.

[0008] The object is achieved by the Coriolis flowmeter according to claim 1. The Coriolis flowmeter according to the invention for determining a time-varying process variable of a flowable medium, comprising:

[0009] - a measuring tube for guiding the medium;

[0010] - an excitation system to excite the measuring tube to mechanical vibrations;

[0011] - a sensor system for detecting the mechanical vibrations of the measuring tube, wherein the sensor system is configured to generate at least a first sensor signal and a second sensor signal,

[0012] - a measuring and / or operating circuit, in particular formed by means of at least one microprocessor, wherein the measuring and / or operating circuit is configured to operate the excitation system with an excitation signal, wherein the measuring and / or operating circuit comprises a first adaptive filter with a filter coefficient a, which is configured to receive the first sensor signal and generate a filtered first sensor signal, wherein the measuring and / or operating circuit (5) comprises a second adaptive filter with a filter coefficient b, which is configured to receive the second sensor signal s2 and generate a filtered second sensor signal s2*, wherein the measuring and / or operating circuit comprises a regulator circuit which is configured to control the filtered first sensor signal s1* and the filtered second sensor signal s2*,or to receive a variable derived from the filtered first sensor signal s1* and the filtered second sensor signal s2*, wherein the control circuit is configured to control the filter coefficient a and / or the filter coefficient b based on the filtered first sensor signal s1* and the filtered second sensor signal s2*, or a variable derived from the filtered first sensor signal s1* and the filtered second sensor signal s2*, such that a control criterion is met, wherein the measuring and / or operating circuit is configured to generate a first measured value representing the process variable from the filter coefficient a and / or the filter coefficient b.

[0013] This means that the first measured value representing the process variable (e.g. mass flow, viscosity, density) is no longer determined analytically, but is derived from the two sensor signals and the filter coefficient a and / or b determined via the control. By controlling the adaptive first filter via the filter coefficient a and the adaptive second filter via the filter coefficient b, for example in such a way that the filtered first sensor signal s1* agrees with the filtered second sensor signal s2* within tolerance limits, the information of the first measured value representing the process variable is projected onto the filter coefficient a and / or b. The filter coefficient a and / or the filter coefficient b therefore describes the influence of the process variable to be determined on the sensor signal and is / or are thus proportional to it.If the first measured value representing the process variable is determined as a function of the filter coefficient a and / or the filter coefficient b, not only the measurement error is reduced, but also the need for a precise synchronization of the driver frequency f with the phase difference A <p. Somit wird verhindert, dass es bei starken Frequenzfluktuationen zu dynamischen Nullpunkt verschiebungen kommt.

[0014] Advantageous embodiments of the invention are the subject of the subclaims.

[0015] One embodiment provides that the controller circuit is configured to determine the filter coefficient a and / or the filter coefficient b by means of a least mean squares algorithm and / or by means of a normalized least mean squares algorithm and / or by means of a recursive least squares algorithm and / or a linear or non-linear gradient method.

[0016] The regulator circuit is preferably located close to the sensor system so that the sensor signal travels only a short distance to the regulator circuit. Furthermore, the sensor signal is preferably provided to the regulator circuit immediately after generation, eliminating the time delay that would otherwise occur if the sensor signal first had to pass through the electronic components to generate the phase difference.

[0017] One embodiment provides that the controller circuit comprises a PID controller which is configured to control the filter coefficient a and / or the filter coefficient b on the basis of the filtered first sensor signal s1* and the filtered second sensor signal s2* or the variable derived from the filtered first sensor signal s1* and the filtered second sensor signal s2* such that the control criterion is met.

[0018] One embodiment provides that the process variable includes the mass flow of the medium.

[0019] One embodiment provides that the excitation signal has a driver frequency f, wherein the driver frequency f is not included in the determination of the first measured value representing the mass flow of the medium. One embodiment provides that the control criterion includes whether a deviation between the filtered first sensor signal s1* and the filtered second sensor signal s2* assumes a sensor signal setpoint or is smaller than a sensor signal limit.

[0020] One embodiment provides that the measuring and / or operating circuit is designed to detect a phase difference 4 <p zwischen dem gefilterten ersten Sensorsignal s1* und dem gefilterten zweiten Sensorsignal s2* zu ermitteln, wobei die abgeleitete Größe der Phasendifferenz 4<p entspricht.

[0021] One embodiment provides that the control criterion includes that the phase difference 4 <p einem Phasendifferenz-Sollwert und / oder kleiner einem Phasendifferenz-Grenzwert entspricht.

[0022] One embodiment provides that a calibration factor k, which is determined in particular at the factory, is additionally included in the generation of the first measured value representing the process variable, in particular the mass flow.

[0023] One embodiment provides that the measuring and / or operating circuit is configured to determine a current process state from the filter coefficient a and / or from the filter coefficient b and optionally output it.

[0024] One embodiment provides that the current process state includes the presence of gas bubbles in the medium.

[0025] One embodiment provides that the measuring and / or operating circuit is designed to:

[0026] - in a first operating mode, a second measured value representing the process variable as a function of a phase difference <p zwischen dem ersten Sensorsignal bzw. dem gefilterten ersten Sensorsignal s1* und dem gefilterten zweiten Sensorsignal s2* und der Treiberfrequenz f zu bestimmen und auszugeben,

[0027] - in a second operating mode, to determine and output the first measured value representing the process variable as a function of the filter coefficient a and / or the filter coefficient b.

[0028] One embodiment provides that the measuring and / or operating circuit is configured to switch from the first operating mode to the second operating mode when a deviation between the first measured value and the second measured value assumes a target value and / or lies outside a tolerance range.

[0029] One embodiment provides that the measuring and / or operating circuit is configured to determine the presence of gas bubbles by comparing a signal representing the first measured value and a signal representing the second measured value.

[0030] One embodiment provides that the measuring and / or operating circuit is designed to:

[0031] - a second measured value representing the process variable, in particular the mass flow, as a function of a phase difference A <p zwischen dem gefilterten ersten Sensorsignal s1* bzw. ersten Sensorsignal und dem gefilterten zweiten Sensorsignal s2* bzw. des zweiten Sensorsignal s2 und der Treiberfrequenz f zu bestimmen,

[0032] - to correct the second measured value as a function of the filter coefficient a and / or the filter coefficient b, or the first measured value, and

[0033] - output the corrected second measured value.

[0034] One embodiment provides that the first filter is designed such that the mathematical relationship between the first sensor signal and the filtered first sensor signal can be described via a transfer function H (s) = (1 - a • s) with a Laplace index s.

[0035] One embodiment provides that the first filter is designed such that the mathematical relationship between the first sensor signal s1 and the filtered first sensor signal s1* can be described via a transfer function H(s) = (1 - a • s) / (l + as) with a Laplace index s.

[0036] One embodiment provides that the first filter is designed such that the mathematical relationship between the first sensor signal s1 and the filtered first sensor signal s1* is determined via a transfer function H(s) = (1 + a) / 2 + (1 - a) / 2 • z -1 , where z is a z-variable of a discrete system.

[0037] One embodiment provides that the second filter is designed such that the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* can be described via a transfer function H (s) = (1 + b • s) with a Laplace index s.

[0038] One embodiment provides that the second filter is designed such that the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* is determined via a transfer function H (s) = (1 - b) / 2 + (1 + b) / 2 ■ z -1 , where z is a z-variable of a discrete system. One embodiment provides that the second filter is designed such that the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* is determined via a transfer function H(s) = % + % * z -1 , where z is a z-variable of a discrete system.

[0039] One embodiment provides that the second filter is designed such that the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* can be described via a transfer function H(s) = 1.

[0040] One embodiment provides that a = b.

[0041] One embodiment provides that the first adaptive filter and / or the second adaptive filter, in particular each, is an all-pass filter.

[0042] The invention is explained in more detail with reference to the following figures. They show:

[0043] Fig. 1 : a diagram of a state-of-the-art Coriolis flowmeter; and

[0044] Fig. 2 : a diagram of two Coriolis flowmeters according to the invention.

[0045] Fig. 1 shows a schematic diagram of a prior art Coriolis flowmeter 1. The Coriolis flowmeter 1 for determining a time-varying process variable of a flowable medium comprises a measuring tube 2 for conveying the medium. The figure shows precisely one straight measuring tube 3. However, the use of curved and / or multiple measuring tubes is already known. The core concept of the invention can be applied to any shape and number of measuring tubes.

[0046] In contact with the measuring tube 2 is an excitation system 3 for exciting the measuring tube 2 to mechanical vibrations. One or more excitation coils per measuring tube are suitable for this purpose. These are arranged by means of a holding device on the measuring tube, in the housing of the Coriolis flowmeter, or in a specially provided arrangement inside the housing. The excitation coil is generally in contact with a magnet arranged directly on the measuring tube or via a holding device on the measuring tube. However, different excitation systems are also known. For example, the excitation system can also be in mechanical contact with the measuring tube 2 and be designed and configured to transmit its own vibration behavior to the measuring tube 2 directly or indirectly. The nature of the excitation system 3, however, is not essential to the invention.

[0047] The Coriolis flowmeter 1 further comprises a sensor system 4 for detecting the mechanical vibrations of the measuring tube 2. The sensor system 4 typically comprises two sensor coils per measuring tube, each of which interacts with a magnet arranged on the measuring tube 2 or another measuring tube (not shown). The sensor coils can - like the excitation coils - be arranged by means of a holding device on the measuring tube 2, in the housing (not shown) of the Coriolis flowmeter 1, or in a specially provided arrangement (not shown) inside the housing. The sensor coils are typically arranged offset from one another in the direction of flow of the medium. The excitation coil is arranged between the two sensor coils in the direction of flow of the medium. However, different sensor systems are also known. For example, the mechanical vibrations of the measuring tube 2 can also be detected using optical sensors.The nature of the sensor system 4 is not essential to the invention. The sensor system 4 is configured to generate at least a first sensor signal s1 and a second sensor signal s2, wherein the first sensor signal s1 and the second sensor signal s2 describe the current vibration behavior of the measuring tube 2 at two different positions offset in the flow direction.

[0048] In the illustrated embodiment, the sensor system 4 comprises two sensor coils, and the excitation system comprises one excitation coil. The positioning of the two sensor coils and the excitation coil is chosen for the purpose of a clearer representation of the diagram and does not correspond to an arrangement actually required for the implementation of the invention. The first sensor signal s1 is provided to one of the two sensor coils, and the second sensor signal s2 is provided to the corresponding other sensor coil.

[0049] The excitation system 3 and the sensor system 4 are connected to a measuring and / or operating circuit 5, in particular comprising at least one microprocessor and electronic components (for example comprising a transistor, an electrical resistor, a capacitor, a mixer, a filter and / or a microcontroller). In the illustrated embodiment, the measuring and / or operating circuit 5 comprises a control unit 6, which is configured to provide an excitation signal with a driver frequency f and an excitation amplitude / 0 and thus to operate the excitation system. In the illustrated embodiment, the excitation signal can be described by I exc = I o ■ cos(2nft), where the excitation amplitude is a maximum excitation coil current and I exc the time-dependent current excitation coil current. The driver frequency f and the excitation amplitude I oare controllable variables. The control unit 6 is designed to control the excitation amplitude I oand to provide the time-varying (periodic) component of the excitation signal - in the form of cos(2nft) - to a mixer 16, which creates the excitation signal from the two parts and forwards it to the excitation system 3. Furthermore, the control unit 6 is electrically connected to four further mixers 9a-d. The control unit 6 is configured to provide a cos(27rft) signal to the mixers 9a, 9c and a sin(27rft) signal to the mixers 9b, 9c. Furthermore, the control unit 6 is configured to transmit the current driver frequency f to a computing unit 8. The computing unit 8 is also part of the measuring and / or operating circuit 5 and is configured to determine the mass flow m at least as a function of the provided driver frequency f. A suitable mathematical equation for this purpose is introduced in the introduction to the description. The driver frequency f is output oris used to determine further process variables.

[0050] The first sensor signal s1 can be described by sl = sl • cos(2nft + p ). <p rthe first phase and sl the first signal amplitude. The first sensor signal s1 goes to the, in particular multiplicative, mixers 9a, 9b for frequency conversion. The mixer 9a is configured to apply a sine component to the first sensor signal s1. For example, the mixer 9a can be configured to multiply the first sensor signal s1 by a sine function (sin 2nft). The mixer 9b is configured to apply a cosine component to the first sensor signal s1. For example, the mixer 9b can be configured to multiply the first sensor signal s1 by a cosine function (cos(2nft). The result of the two mixers 9a, 9b is each provided to a filter 10a, 10b. The filters 10a, 10b can be programmable low-pass filters, for example. These can be designed to eliminate the 2f component of the sensor signal.Furthermore, the filters 10a, 10b are configured to limit the bandwidth of the incoming sensor signal in order to reduce the noise component. The filtered results are provided to a computing unit 11a, which is suitable and configured to execute an algorithm. The algorithm can be, for example, an iterative algorithm, in particular a coordinate rotation digital computer algorithm, with which mathematical functions can be executed. The algorithm is configured and configured to carry out the first phase <p. r and to determine the first signal amplitude sl. The first signal amplitude sl can be output or used to determine another process variable.

[0051] The second sensor signal s2 can be described by s2 = s2 • cos(2nft + cp2~). Where cp2 is the second phase and s2 is the second signal amplitude. The second phase <p2ist bei fließenden Medium um eine Phasendifferenz A<p von der ersten Phase <p roffset. The second sensor signal s2 goes to the, in particular multiplicative, mixers 9c, 9d. The mixer 9c is configured to apply a sine component to the second sensor signal s2. For example, the mixer 9a can be configured to multiply the second sensor signal s2 by a sine function sin(2nft). The mixer 9b is configured to apply a cosine component to the second sensor signal s2. For example, the mixer 9b can be configured to multiply the second sensor signal s2 by a cosine function cos(2nft). The result of the two mixers 9c, 9d is each provided to a filter 10c, 10d. The filters 10c, 10d can be low-pass filters, for example. The filtered results are provided to a computing unit 11b, which is configured to execute an algorithm.The algorithm may, for example, be an iterative algorithm, in particular a Coordinate Rotation Digital Computer algorithm, with which mathematical functions can be executed. The algorithm is designed and configured to carry out the second phase <p2und die zweite Signalamplitude §2 zu ermitteln. Die zweite Signalamplitude §2 kann ausgegeben bzw. für die Bestimmung einerweiteren Prozessgröße eingesetzt werden. Die erste Phase <p. r and the second phase <p2werden jeweils an einem Filter 12a, 12b bereitgestellt. Die Filter 12a, 12b sind dazu eingerichtet, den jeweiligen Rauschanteile der ermittelten Phasen zu reduzieren. Bei den Filtern 12a, 12b kann es sich beispielsweise um Tiefpass-Filter handeln.

[0052] The measuring and / or operating circuit 15 further comprises a subtractor 13. The first phase <p und die zweite Phase p2gehen in den Subtrahierer 13 ein. Der Subtrahierer 13 ist dazu eingerichtet, die Phasendifferenz A<p - die proportional zum Massenstrom m ist - zwischen der ersten Phase <p und der zweiten Phase p2zu bestimmen und an eine Recheinheit 8 bereitzustellen. Die Recheneinheit 8 ist dazu eingerichtet, den Massenstrom m in Abhängigkeit der Phasendifferenz A<p und der bereitgestellten Treiberfrequenz f zu bestimmen. Der Massenstrom m wird basierend auf der Gleichung m = k • tan( <p / 2) / 2nf bestimmt.

[0053] Fig. 2 shows a schematic of two Coriolis flowmeters according to the invention. The first design is represented by the dashed lines, and the second design by the solid lines.

[0054] According to the first embodiment, the first sensor signal s1 is provided to a first adaptive filter 7a. The first filter 7a can be an all-pass filter. The all-pass filter is a signal processing filter that passes all frequencies equally but changes the phase relationship between the different frequencies. The first filter 7a is configured to receive the first sensor signal s1 and generate a filtered first sensor signal s1*. For the transfer function H(s), with which the first sensor signal s1 is converted into the filtered first sensor signal s1*, H(s) = (1 - a • s). s is the Laplace index.

[0055] Alternatively, the mathematical relationship between the first sensor signal s1 and the filtered first sensor signal s1* can also be described by a transfer function H(s) = (1 - a • s) / (l + as) with a Laplace index s.

[0056] Alternatively, the mathematical relationship between the first sensor signal s1 and the filtered first sensor signal s1* can be expressed via a transfer function H(s) = (1 + a) / 2 + (1 - a) / 2 • z -1 be describable. In this case, z is a z-variable of a discrete system.

[0057] According to the first embodiment, the second sensor signal s2 is provided to a second adaptive filter 7b. The second filter 7b can also be an all-pass filter. The all-pass filter is a signal processing filter that passes all frequencies equally, but changes the phase relationship between the different frequencies. The second filter 7b is configured to receive the second sensor signal s2 and generate a filtered second sensor signal s2*. The transfer function H(s) with which the second sensor signal s2 is converted into the filtered second sensor signal s2* is such that H(s) = (1 + b • s). S is also the Laplace index. Alternatively, the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* can be expressed via a transfer function H(s~) = (1 - b~) / 2 + (1 + b) / 2 ■ z -1be describable. In this case, z is a z-variable of a discrete system.

[0058] Alternatively, the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* can be expressed via a transfer function H(s~) = % + % * z -1 be describable. In this case, z is a z-variable of a discrete system.

[0059] Alternatively, the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* can be described by a transfer function H(s~) = 1.

[0060] The measuring and / or operating circuit 5 has a controller circuit 15 configured to control the filter coefficient a and / or the filter coefficient b based on the filtered first sensor signal s1* and the filtered second sensor signal s2*, or a variable derived from the filtered first sensor signal s1* and the filtered second sensor signal s2*, such that a control criterion is met. The control criterion can be a deviation between the filtered first sensor signal s1* and the filtered second sensor signal s2*, which must assume a sensor signal target value or be smaller than a sensor signal limit value.According to the invention, the controller circuit 15 can be configured to determine the filter coefficient a and / or the filter coefficient b by means of a least mean squares algorithm and / or by means of a normalized least mean squares algorithm and / or by means of a recursive least squares algorithm and / or a linear or non-linear gradient method.

[0061] Alternatively, the controller circuit 15 may comprise a PID controller which is configured to control the filter coefficient a and / or the filter coefficient b based on the filtered first sensor signal s1* and the filtered second sensor signal s2* or the variable derived from the filtered first sensor signal s1* and the filtered second sensor signal s2* such that the control criterion is met.

[0062] The measuring and / or operating circuit 5 comprises a computing unit 14, which is configured to generate a first measured value for the current mass flow through the pipeline from the filter coefficient a and / or the filter coefficient b. To determine the first measured value representing the mass flow, a calibration factor k, which is determined in particular at the factory, is also used. The equation a = k • m applies. F or b = k • m F Thus, the driver frequency f is not included in the determination of the first measured value representing the mass flow of the medium. Alternatively or additionally, the measuring and / or operating circuit 5, in particular the computing unit 14, can be configured to determine a current process state from the filter coefficient a and / or from the filter coefficient b and optionally output it. An example of the process state to be detected is the presence of gas bubbles in the medium.

[0063] In the second embodiment, the measuring and / or operating circuit 5 is configured to determine a phase difference Acp between the filtered first sensor signal s1* and the filtered second sensor signal s2*. For this purpose, the first sensor signal s1 is provided to the adaptive first filter, where it is filtered. The filtered sensor signal s*1 passes through the mixers 9a, 9b, where it is mixed as described for the prior art. After mixing, the filtered first sensor signal s*1, which has a sine component, passes through a filter 10a. The filter 10a is configured to eliminate the 2f component of the mixed sensor signal s*1 and reduce the noise component.

[0064] It is then provided to a computing unit 11a, which is configured to determine the first signal amplitude s*1 of the filtered first sensor signal. The filtered first sensor signal s*1, which is subjected to a cosine component, passes through a filter 10b. The filter 10b, like the filter 10a, is configured to eliminate the 2f component of the mixed sensor signal s*1 and to reduce the noise component. It is then provided to a computing unit 11b, which is configured to determine the filtered first phase <p*i des gefilterten ersten Sensorsignals zu bestimmen. Die gefilterte erste Phase <p*i durchläuft weiterhin einen Filter 12a, bevor sie an einem Subtrahierer 13 bereitgestellt wird.

[0065] To determine the phase difference A <p wird das zweite Sensorsignal s2 an einem adaptiven zweiten Filter 7b bereitgestellt wo es gefiltert wird. Das gefilterte Sensorsignal s*1 durchläuft die Mischer 9c, 9d, die Filter 10c, 10d, die Recheneinheit 11 b und den Filter 12b. Die Verarbeitung des gefilterten zweiten Sensorsignales s2* entspricht der in der Figurenbeschreibung beschriebenen Verarbeitung. Die ermittelte zweite Phase <p2 wird am Subtrahierer bereitgestellt. Der Subtrahierer 13 ist dazu eingerichtet die Phasendifferenz A<p zwischen der gefilterten ersten Phase <p* und der zweiten Phase <p2 zu ermitteln und an die Regeleinheit 15 bereitzustellen. Die Regeleinheit 15 ist dazu eingerichtet den Filterkoeffizienten a so zu regeln, dass die Phasendifferenz A<p einem Phasendifferenz-Sollwert und / oder kleiner einem Phasendifferenz-Grenzwert entspricht.In particular, the filter coefficient a and / or the filter coefficient b are controlled so that the phase difference A <p minimal oder Null ist. Ebenfalls wie in der vorherigen Ausgestaltung ist die Recheneinheit 14 dazu eingerichtet, die den Massenstrom repräsentierende Messwerte in Abhängigkeit des Filterkoeffizienten a und / oder des Filterkoeffizienten b und einem Kalibrierfaktor k zu bestimmen.

[0066] A third embodiment combines the processes of the two previous embodiments and groups them into different operating modes. In a first operating mode, a second measured value representing the process variable is determined as a function of a phase difference <p zwischen dem ersten Sensorsignal s1 bzw. dem gefilterten ersten Sensorsignal s1* und dem zweiten Sensorsignal s2 bzw. dem gefilterten zweiten Sensorsignal s2* und der Treiberfrequenz f bestimmt und optional ausgegeben. Bei dem zweiten Messwert kann es sich um den Massenstrom handeln. In einem zweiten Betriebsmodus wird der die Prozessgröße repräsentierende erste Messwert in Abhängigkeit des Filterkoeffizienten a und / oder des Filterkoeffizienten b bestimmt und optional ausgegeben.The measuring and / or operating circuit 5 is configured to switch from the first operating mode to the second operating mode when a deviation between the first measured value and the second measured value reaches a target value and / or lies outside a tolerance range. The second measured value can be corrected depending on the filter coefficient a and / or the filter coefficient b or the first measured value, and the corrected second measured value can be output.

[0067] LIST OF REFERENCE SYMBOLS

[0068] 1 Coriolis flowmeter

[0069] 2 Measuring tube 3 Excitation system

[0070] 4 Sensor system

[0071] 5 Measuring and / or operating circuit

[0072] 6 Control unit

[0073] 7 AllPass Filter 8 Computing Unit

[0074] 9i mixer

[0075] 10i Filter

[0076] 11i computing unit

[0077] 12i Filter 13 Subtractor

[0078] 14 Computing unit

[0079] 15 Regulator circuit

[0080] 16 mixers

Claims

PATENT CLAIMS 1. Coriolis flowmeter (1) for determining a time-varying process variable of a flowable medium, comprising: - a measuring tube (2) for guiding the medium; - an excitation system (3) for exciting the measuring tube (2) to mechanical vibrations; - a sensor system (4) for detecting the mechanical vibrations of the measuring tube (2), wherein the sensor system (4) is designed to generate at least a first sensor signal s1 and a second sensor signal s2, - a measuring and / or operating circuit (5), in particular formed by means of at least one microprocessor, wherein the measuring and / or operating circuit (5) is configured to operate the excitation system with an excitation signal, wherein the measuring and / or operating circuit (5) comprises a first adaptive filter (7a) with a filter coefficient a, which is configured to receive the first sensor signal s1 and to generate a filtered first sensor signal s1*, wherein the measuring and / or operating circuit (5) comprises a second adaptive filter (7b) with a filter coefficient b, which is configured to receive the second sensor signal s2 and to generate a filtered second sensor signal s2*, wherein the measuring and / or operating circuit (5) comprises a regulator circuit (15) which is configured to control the filtered first sensor signal s1* and the filtered second sensor signal s2*,or to receive a variable derived from the filtered first sensor signal s1* and the filtered second sensor signal s2*, wherein the controller circuit (15) is configured to control the filter coefficient a and / or the filter coefficient b based on the filtered first sensor signal s1* and the filtered second sensor signal s2*, or a variable derived from the filtered first sensor signal s1* and the filtered second sensor signal s2*, such that a control criterion is met, wherein the measuring and / or operating circuit (5) is configured to generate a first measured value representing the process variable from the filter coefficient a and / or from the filter coefficient b.

2. Coriolis flowmeter according to claim 1, wherein the controller circuit (15) is configured to determine the filter coefficient a and / or the filter coefficient b by means of a least mean squares algorithm and / or by means of a normalized least mean squares algorithm and / or by means of a recursive least squares algorithm and / or a linear or non-linear gradient method.

3. Coriolis flowmeter according to claim 1, wherein the controller circuit (15) comprises a PID controller which is configured to control the filter coefficient a and / or the filter coefficient b on the basis of the filtered first sensor signal s1* and the filtered second sensor signal s2* or the variable derived from the filtered first sensor signal s1* and the filtered second sensor signal s2* such that the control criterion is met.

4. Coriolis flowmeter according to one of the preceding claims, wherein the process variable comprises the mass flow of the medium.

5. Coriolis flowmeter according to claim 4, wherein the excitation signal has a driver frequency, wherein the driver frequency is not included in the determination of the first measured value representing the mass flow of the medium.

6. Coriolis flowmeter according to one of the preceding claims, wherein the control criterion comprises that a deviation between the filtered first sensor signal s1* and the filtered second sensor signal s2* assumes a sensor signal setpoint or is smaller than a sensor signal limit value.

7. Coriolis flowmeter according to one of the preceding claims, wherein the measuring and / or operating circuit (5) is designed to measure a phase difference A <p zwischen dem gefilterten ersten Sensorsignal s1* und dem gefilterten zweiten Sensorsignal s2* zu ermitteln, wobei die abgeleitete Größe der Phasendifferenz A<p entspricht.

8. Coriolis flowmeter according to claim 7, wherein the control criterion comprises that the phase difference A <p einem Phasendifferenz- Sollwert und / oder kleiner einem Phasendifferenz-Grenzwert entspricht.

9. Coriolis flowmeter according to one of the preceding claims, wherein a calibration factor k, which is determined in particular at the factory, is additionally included in the generation of the first measured value representing the process variable, in particular the mass flow.

10. Coriolis flowmeter according to one of the preceding claims, wherein the measuring and / or operating circuit (5) is configured to determine a current process state from the filter coefficient a and / or from the filter coefficient b and optionally output it.

11. Coriolis flowmeter according to claim 10, wherein the current process state includes the presence of gas bubbles in the medium.

12. Coriolis flowmeter according to one of claims 4 to 11, wherein the measuring and / or operating circuit (5) is arranged to: - in a first operating mode, a second measured value representing the process variable as a function of a phase difference A <p zwischen dem ersten Sensorsignal s1 bzw. dem gefilterten first sensor signal s1* and the filtered second sensor signal s2* and the driver frequency f, - in a second operating mode, to determine and output the first measured value representing the process variable as a function of the filter coefficient a and / or the filter coefficient b.

13. Coriolis flowmeter according to claim 12, wherein the measuring and / or operating circuit (5) is configured to switch from the first operating mode to the second operating mode when a deviation between the first measured value and the second measured value assumes a desired value and / or lies outside a tolerance range.

14. Coriolis flowmeter according to claim 13, wherein the measuring and / or operating circuit (5) is configured to determine the presence of gas bubbles by comparing a signal representing the first measured value and a signal representing the second measured value.

15. Coriolis flowmeter according to one of the preceding claims, wherein the measuring and / or operating circuit (5) is arranged to: - a second measured value representing the process variable, in particular the mass flow, as a function of a phase difference A <p zwischen dem gefilterten ersten Sensorsignal s1* bzw. ersten Sensorsignal s1 und dem gefilterten zweiten Sensorsignal s2* bzw. des zweiten Sensorsignal s2 und der Treiberfrequenz f zu bestimmen, - to correct the second measured value depending on the filter coefficient a and / or b, or the first measured value, and - output the corrected second measured value.

16. Coriolis flowmeter according to one of the preceding claims, wherein the first filter is designed such that the mathematical relationship between the first sensor signal s1 and the filtered first sensor signal s1* can be described via a transfer function H (s) = (1 - a • s) with a Laplace index s.

17. Coriolis flowmeter according to one of claims 1 to 15, wherein the first filter is designed such that the mathematical relationship between the first sensor signal s1 and the filtered first sensor signal s1* can be described via a transfer function H(s) = (1 - a • s) / (l + as) with a Laplace index s.

18. Coriolis flowmeter according to one of claims 1 to 15, wherein the first filter is designed such that the mathematical relationship between the first sensor signal s1 and the filtered first sensor signal s1* is determined via a transfer function H(s) = (1 + a) / 2 + (1 - a) / 2 • z -1can be described, where z is a z-variable of a discrete system.

19. Coriolis flowmeter according to one of the preceding claims, wherein the second filter is designed such that the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* can be described via a transfer function H(s) = (1 + b • s) with a Laplace index s.

20. Coriolis flowmeter according to one of claims 1 to 18, wherein the second filter is designed such that the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* is determined via a transfer function H(s)' = (1 - b) / 2 + (1 + b) / 2 ■ z -1 can be described, where z is a z-variable of a discrete system.

21. Coriolis flowmeter according to one of claims 1 to 18, wherein the second filter is designed such that the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* is determined via a transfer function H(s) = % + % * z -1 can be described, where z is a z-variable of a discrete system.

22. Coriolis flowmeter according to one of claims 1 to 18, wherein the second filter is designed such that the mathematical relationship between the second sensor signal s2 and the filtered second sensor signal s2* can be described by a transfer function H(s) = 1.

23. A Coriolis flowmeter according to any one of the preceding claims, wherein a = b.

24. A Coriolis flowmeter according to any one of the preceding claims, wherein the first adaptive filter and / or the second adaptive filter are, in particular, each an all-pass filter.

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